PHA-stimulated human peripheral lymphocytes were used as a model system for assessing the in vitro effects of calcium cyclamate. Techniques of autoradiography, cytological staining, cell counting, liquid scintillation and karyotyping were used to study the cytogenetic damage and biochemical effects of calcium cyclamate when assayed in 24 hour intervals for 96 hours. The cells were exposed to 10(-2) and 10(-3) molar concentrations of calcium cyclamate in TC 199 medium with fetal calf serum and antibiotics. These studies were carried out in three (3) phases. Phase I was primarily orientation studies of the effects of cyclamates and included running preliminary test checks, the establishment of parameters of dosage, assessing growth patterns and selecting key chromosomal aberrations. Sixty four (64) of the metaphase spreads showed morphologically detectable changes and aberrations. It was also noted that the addition of cyclamate increased mitotic rate of lymphocyte cells in cultures. Phase III arranged research designs to determine more precise characterization of chromosomal observations and morphological effects. Among other findings it was noted that of 13 types of observations only ten were found in the experimental group. The introduction of cyclamates increased the stability of the leucocyte cultures. These studies reinforced the findings on the increase of mitotic rate. Phase III extended protocols to include autoradiography and scintillation counting. It was determined that calcium cyclamate impaired the synthesis of deoxribonunucleic acid (as depicted by decreased incorporation of tritiated thymidine), reduced grain counts in autoradiographs and increased chromosome aberrations in cyclamate treated PHA stimulated peripheral blood lymphocytes in vitro. Morphological changes and growth rates showed significant effects. These studies indicate that calcium cyclamate has variable significant effects on leucocytes growth and chromosome morphology.